Research On Crack Propagation Path And Assessment Life Of Joint Of Railway Steel Bridge Considering Composite Cracks

Due to the defects of welding and cyclic stress,the monolithic joints of the railway steel truss bridge are prone to fatigue problems under the repeated action of train loads,so the fatigue failure of the joints becomes the main form of damage to the long-span steel truss bridges.Research on the structural failure process and failure time of the steel bridge under the initial crack,and put forward the simulation of composite crack propagation path and the assessment of fatigue crack propagation life of railway steel truss bridge,it is of great significance for ensuring the safety of steel bridges and preventing the occurrence of catastrophic accidents.In this paper,the combination of theory and practice research methods is used.Taking a railway steel truss bridge as the project background,the finite element simulation of the whole bridge structure and the joint contains initial crack model of railway steel truss bridge is established,dynamic response of whole bridge structure and the joint contains initial crack model are obtained,and the crack propagation path simulation and the assessment of fatigue crack growth life of the integrated joint are deeply studied.Combined with the current research status,the simulation of crack propagation path and the assessment crack propagation life of railway steel truss bridges are studied.The main contents are as follows:Firstly,the current domestic and international research progresses are elaborated in detail,and the current research deficiencies are explained.The assumptions of crack propagation path simulation and extended life assessment for railway steel truss bridges considering composite cracking effects are proposed.The classification criteria of three-dimensional cracks,the stress field function at the crack tip,the calculation method of stress intensity factor,and the fracture criterion of composite cracks are mainly described.The crack propagation path simulation and the method of crack propagation life assessment considering the type I and II cracks are proposed.The process of the crack propagation path simulation and the crack propagation life assessment with considering the composite I-II cracks propagation is described in detail.The ANSYS general finite element software is used to simulate the crack propagation path of the unilateral oblique crack model.The program of the crack propagation life assessment based on the four-parameters full-range FORMAN formula is programmed by using MATLAB,the calculation results is compared with the related literature studies,and the correctness of the proposed method is verified.Secondly,the engineering background of this steel truss bridge is briefly introduced.The FEM of the integral shell of the railway steel truss bridge is established based on the sub-model method by using ANSYS.The dynamic load of the train crossing the bridge is calculated according to the actual freight train parameters by using MTLAB.By applying the train bridge load to the finite element model of the integral shell of railway steel truss bridge,the dynamic response of the finite element model of the integral shell is calculated.The location,length,and direction of the initial cracks is assessed which may occur at the big chords.The FEM of the node entity with initial crack defect is established,and its dynamic response is calculated using the sub-model method.Finally,the equivalent stress amplitude at the boundary of solid model is obtained by rain-flow counting method and Miner equivalent stress method.According to the proposed method,the crack propagation path and the crack propagation life of the weld toe at the connection point between the gusset plate and the box girder are studied.In summary,this method can accurately simulate the crack propagation path and assess the fatigue crack growth life of the railway steel truss bridge considering the effect of composite crack under freight trains load in this paper.So,it is of great significance for the operation and maintenance of steel bridges to predict the development trend of fatigue cracks,evaluate the crack propagation life of railway steel truss bridges,evaluate the structural safety and prevent the occurrence of catastrophic accidents.